In recent years, in a semiconductor device manufacturing process, a dry etching technique called chemical oxide removal (COR) draws attentions as an alternative fine etching method for dry etching or wet etching. A hydrogen fluoride (HF) gas alone or a combination of the HF gas and an ammonia (NH3) gas is used to etch an oxide such as a silicon oxide (SiO2).
The COR process is a low-damage technique of etching the oxide without generating plasma within a chamber. For this reason, the COR process is recently under consideration as a way to etch a silicon nitride (SiN) film. As an etching gas used in etching the SiN film without generating plasma within the chamber, a combination of an HF gas and an F2 gas is under consideration.
However, in a semiconductor wafer, an SiN film is formed adjacent to silicon (Si) included in a polysilicon (poly-Si) film, an Si substrate or the like, or an SiO2 film in many cases. In this situation, when the SiN film is etched with the combination of the HF gas and the F2 gas, the SiO2 film may be etched by the HF gas and an NH3 gas generated as reaction products at a low temperature, while the poly-Si film may be etched at a high temperature. This causes a problem in that it is difficult to etch the SiN film with respect to the SiO2 film and the poly-Si film with high selectivity.
Some embodiments of the present disclosure provide an etching method which is capable of etching a silicon nitride film with respect to at least one of a silicon oxide film and a polysilicon film with high selectivity, without generating plasma within a chamber.